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rweber
I am casting the same method like you do but I have hairy cracks on the casting surface .
How high temperature do you use for melting wax out and how long do you keep concrete mould in the oven ?
Thank you

Member

I have been doing some lost PLA casting in the last couple years. I use filament called polycast which is designed for this and prints just like PLA, but seems to have similar results to using normal PLA filament, except the fact I can smooth the prints out with isopropyl alcohol. Anyway I think the key to a successful lost PLA casting is good investment material, and having control over the temperature and time of the burnout leading up to the pour. I simply bought a kiln off of craigslist for about 40 bucks and put a programmable ramp and soak timer to control the kiln I bought off of ebay cheap. This process for a part your size will take approximately 6-8hrs I bet, depending on flask size. This helps ensure you have complete burnout, less likely to crack the mold, and correct flask temp when your pouring so the molten metal does not solidify too fast.

The flask size, investment material, and type of metal you are using will determine the temperature and length of time for the burnout, which is not always linear. I think some of my burnout schedules have 8 different steps in them, so you ramp up to certain temps, hold it for a certain amount of time, ramp down, hold it, etc.. All this info will be provided by the investment manufacturer. Ransom and Randolph has investment called plasticast which is specifically designed for lost PLA type casting and I recommend using that.

With all that being said, I still say a prayer everytime I pour because you just never how it will turn out! Lots of trial and error, with even more frustration. Good luck sir!

kadora, I used a temp of 270°C (document says 260-280). It tooks about 3-4 hours. I had also tried a plaster mould and also had cracks. I assumed, that the mould was not dry enough, so I switch to that concrete stuff. But you can try to dry the mold better before melting out. Perhaps a few days on the radiator? I know, time I alwasys an issue, so perhaps put it into the oven at inceaase the temp slowly. Make sure, the wife takes no notice of that ;-)

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where I tried many times with a home made plaster/silica sand mix with a make shift furnace, and I ALWAYS fought cracks. When reading the instructions of the R+R plasticast they say if you are not going to put the mold in the oven within a few hours then to seal it in a ziplock bag with a wet paper towel to keep it moist. because for some reason that can also cause cracking.

Must do dumb things....

The "2nd" piston is the crosshead. It take up the side loading from the connecting rod and allows the piston to be double acting. This way, a double acting, two cylinder steam engine is self starting. This arrangement also gives the same number of power pulses per revolution as an eight cylinder gas engine.

I plan for the engine to run a spin art machine and turned on by the kiddos. They aren't going to understand a non-self starting engine, so I figured I just make one that is. I've also never made an engine in this arrangement, so it'll be a new challenge to which I may or may not suck.

Member

There are two types of soluble filaments: PVA and HIPS. PVA can be used to print soluble parts for suspended pieces. It is used in conjunction with PLA. This dissolves in hot water within a few hours. HIPS can also be used for the support, it prints with ABS. Obvious water soluble plaster can not be used. And before hot metal is pored into the mold the water has to be removed. This is a youtube video of urathane bonded casting sand.